Saw transducer with coplanar waveguide transition

Abstract

Disclosed is a coplanar waveguide (CPW) which is connected directly into abalanced SAW transducer" via a tapered coplanar transmission line. Preferably, the CPW transition feeds directly into the "balanced transducer" such that the ground planes of the CPW taper directly into the outer (grounded) bus bars of the SAW transducer and the center conductor of the CPW feeds directly into the "hot" center electrode structure of the SAW transducer. This preferred structure is shown in FIG. 1. This balanced SAW transducer configuration provides better electrical shielding for lower electromagnetic feedthrough suppression and lower spurious signal levels. Moreover, the acoustic wave generated by this "balanced transducer" configuration provides a more uniform acoustic power distribution because the center conductor of the SAW transducer provides a waveguide effect wherein the acoustic energy tends to follow the slow velocity metal structure, thus forming an acoustic waveguide.

What is claimed is: 
     
       1. A surface acoustic wave transducer disposed on a piezoelectric substrate comprising: a balanced surface acoustic wave transducer, the transducer comprising a central electrode structure, at least a first and second grounded bus bars mounted on either side of the central electrode structure and interdigitated electrodes extending alternately from both bus bars and the central electrode structure;   a coplanar waveguide directly connected to the transducer via tapered conductors, the coplanar waveguide comprising a central conductor which includes a series inductance matching element and at least a first and second ground planes mounted on either side of the central conductor, wherein the coplanar waveguide is connected to the transducer such that the first ground plane is directly connected to the first bus bar, the second ground plane is directly connected to the second bus bar, and the central conductor is directly connected to the central electrode structure.